This invention relates to the agglomeration of fine particulate material into briquets. More particularly it relates to apparatus for forming metallized particulates into briquets which are joined together by a web to form a sheet of connected briquets and breaking the sheet into individual briquets for further processing.
Particulate material is agglomerated by a variety of agglomeration techniques. One such technique is known as briquetting in which particulate solids are compacted between two countercurrently rotating rolls, each having a number of recesses or pockets. Sometimes the pockets on one roll mate with the pockets on another but frequently the pockets on one roll mate with a smooth surface of the other roll. Although in theory each shaped briquet is an entity unto itself and is not connected to any other briquet, in practice a web is formed between adjacent briquets resulting in a continuous briquet strip product issuing from the briquetter rolls. Each briquet is connected in both directions to each succeeding briquet by the web thereby forming a sheet of connected briquets. There must be from one to 10 mm clearance between briquetting rolls, and the web is formed in this region of clearance. Even if the rolls were able to be pressed tightly against one another with no clearance between them, a web would form between briquets as particulate material is not subject to the natural laws of liquid flow. When briquetting rolls begin to wear, the web becomes thicker and more difficult to break than the thinner webs produced by new or freshly ground rolls. The web is more dense and much stronger than the briquets. Breaking tests with metallized iron briquets have shown the connection to be approximately five times as strong as the briquets, and roughly one-half as strong as mild steel plate. When two briquets are broken apart, the connection tears through the briquet, rather than the web. The problem of breaking the briquet sheet into its individual briquets has been a continuing one as is evidenced by U.S. Pat. No. 3,300,815; U.S. Pat. No. 3,593,378; and U.S. Pat. No. 3,986,864.
As a metallized iron briquet sheet leaves the briquetting machine, the hot compacted sheet is relatively plastic and easily bent but difficult to break into individual briquets. Consequently, we have found that it is necessary to cool the briquet sheet to a temperature of 425.degree. C. or lower. At this temperature the physical characteristics of iron are such that it is almost as brittle as it is at ambient temperature. The strength, ductility and elongation properties of iron do not change significantly between room temperature and 425.degree. C. Thus the briquet sheet is easily broken when deformed by an externally applied load. We also found it necessary to bend the cooled briquet sheet at least 10 degress and preferably 15 degrees between adjacent briquets to achieve a break.